The source of bromine that drives polar boundary
layer ozone depletion events (ODEs) is still open to some debate. While ODEs
are generally noted to form under conditions of a shallow stable boundary
layer, observations of depleted air under high wind conditions are taken as
being transport-related. Here we report observations from Antarctica in
which an unusually large cloud of BrO formed over the Weddell Sea. The
enhanced BrO was observed over Halley station in coastal Antarctica,
providing an opportunity to probe the conditions within an active "bromine
explosion" event. On this occasion, enhanced BrO and depleted boundary
layer ozone coincided with high wind speeds and saline blowing snow. We
derive a simple model to consider the environmental conditions that favour
ODEs and find two maxima, one at low wind/stable boundary layer and one at
high wind speeds with blowing snow. Modelling calculations aiming to
reproduce the wider regional or global impacts of ODEs, either via radiative
effects or as a halogen source, will also need to account for high wind
speed mechanisms.